Comparing visual search and eye movements in bilinguals ... · Comparing visual search and eye movements in bilinguals and monolinguals Ileana Ratiu1,2 & Michael C. Hout3 & Stephen

Comparing visual search and eye movementsin bilinguals and monolinguals

Ileana Ratiu1,2& Michael C. Hout3 & Stephen C. Walenchok1

& Tamiko Azuma1 &

Stephen D. Goldinger1

Published online: 15 May 2017# The Psychonomic Society, Inc. 2017

Abstract Recent research has suggested that bilinguals showadvantages over monolinguals in visual search tasks, althoughthese findings have been derived from global behavioral mea-sures of accuracy and response times. In the present study wesought to explore the bilingual advantage by using more sen-sitive eyetracking techniques across three visual search exper-iments. These spatially and temporally fine-grained measuresallowed us to carefully investigate any nuanced attentionaldifferences between bilinguals and monolinguals. Bilingualand monolingual participants completed visual search tasksthat varied in difficulty. The experiments required participantsto make careful discriminations in order to detect targetLandolt Cs among similar distractors. In Experiment 1, par-ticipants performed both feature and conjunction search. InExperiments 2 and 3, participants performed visual searchwhile making different types of speeded discriminations, aftereither locating the target or mentally updating a constantlychanging target. The results across all experiments revealedthat bilinguals and monolinguals were equally efficient atguiding attention and generating responses. These findingssuggest that the bilingual advantage does not reflect a generalbenefit in attentional guidance, but could reflect more efficientguidance only under specific task demands.

Keywords Visual search . Eyemovements . Attentionalcontrol . Bilingualism

Bilingual individuals regularly manage two ormore languagesefficiently. They are able to converse in one language whileinhibiting the other(s), and even switch languages within aconversation with minimal error (Gollan, Sandoval, &Salmon, 2011). Thus, for bilingual individuals, languageselection is theorized to be a near-constant demand on execu-tive resources. Consistent with this view, many studies havesuggested that lifelong bilingualism fosters general cognitiveadvantages. Previous studies have reported a bilingual advan-tage in nonlinguistic tasks that require the inhibition of irrele-vant stimuli (Bialystok, Craik, & Ryan, 2006; Emmorey, Luk,Pyers, & Bialystok, 2008), updating and monitoring of infor-mation (Bialystok, Craik, & Ruocco, 2006; Costa, Hernández,Costa-Faidella, & Sebastián-Gallés, 2009), and shifting orswitching between tasks (Prior & Gollan, 2011; Prior &MacWhinney, 2010).

Previous research has demonstrated that, for bilinguals,lexical items in both languages are always active, regardlessof the language context (e.g., De Groot, Delmaar, & Lupker,2000; Dijkstra, Van Jaarsveld, & Ten Brinke, 1998; Kroll,Bobb, Misra, & Guo, 2008). For instance, when a Spanish–English bilingual thinks about the concept tree, representa-tions for both Btree^ and Bárbol^ will become active. Thespeaker cannot simultaneously say Btree^ and Bárbol,^ sothese items compete for lexical selection. Green andAbutalebi (2013) proposed that bilinguals use multiple adap-tive control mechanisms to resolve the conflict between com-peting language activations, referred to as language control.According to their adaptive-control hypothesis, bilinguals useprocesses such as goal maintenance, interference suppression,response inhibition, and task engagement/disengagement tomanage their languages in different linguistic contexts.These mechanisms are associated with one or more executivefunctions. Although the adaptive-control hypothesis primarilymakes assumptions about language processing, Green and

* Ileana [email protected]

1 Arizona State University, Tempe, AZ, USA2 Midwestern University, Glendale, AZ, USA3 New Mexico State University, Las Cruces, NM, USA

Atten Percept Psychophys (2017) 79:1695–1725DOI 10.3758/s13414-017-1328-3

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Abutalebi suggested that a cognitive advantage may arise forbilinguals because language control requires general cognitivemechanisms that become more efficient under the constantdemands of bilingual life. By virtue of exercising constantlanguage selection, bilinguals may develop general cognitiveor executive function advantages, even in nonlinguistic do-mains (e.g., Bialystok, Craik, & Ryan, 2006).

Executive functions (EFs) denote a set of cognitive process-es responsible for the complex control of thoughts and actions.People require EFs when suppressing interference fromdistracting stimuli, holding goals in memory, or switchingattention between tasks. Individual differences in EF arewell-documented, and these differences often predict perfor-mance in cognitive tasks (Friedman et al., 2006). Closely re-lated to EF is working memory capacity (WMC; see, e.g.,Miyake et al., 2000), which allows individuals to attend togoal-relevant information (Shipstead, Lindsey, Marshall, &Engle, 2014). Although there is ongoing debate regardingthe exact relationship between WMC and EF, higher WMCis associated with better performance across many cognitivetasks (e.g., Kane & Engle, 2002). WMC may be affected bysecond language acquisition. Macnamara and Conway (2014)found that some aspects of WMC improved with second lan-guage acquisition and concluded that bilinguals with highlanguage control demands (i.e., frequent use of both lan-guages) have enhanced cognitive control and WMC.

The benefits of higher WMC and bilingualism may alsoextend to visual search tasks (e.g., Friesen, Latman, Calvo, &Bialystok, 2015; Hernández, Costa, & Humphreys, 2012;Poole & Kane, 2009; Sobel, Gerrie, Poole, & Kane, 2007).Visual search is a flexible paradigm that has the potential tohelp address theoretical questions regarding EF. Searchingrequires people to judiciously guide attention to the right lo-cations while simultaneously ignoring distracting information.It also requires that people maintain task goals in memory, andmatch mental templates to visual input. Search difficulty canbe manipulated by varying the number of items in the display,changing target discrimination difficulty among thedistractors, or imposing simultaneous tasks. Previous researchhas shown that people with high WMC located targets fasterthan people with low WMC when the targets were embeddedamong highly similar distractors (e.g., Sobel et al., 2007), andwhile holding multiple potential target locations in workingmemory for long durations (e.g., Poole & Kane, 2009).However, when targets were highly discriminable fromdistractors, no WMC advantage was observed (e.g., Kane,Poole, Tuholski, & Engle, 2006).

Relatedly, there is evidence that bilinguals may have anadvantage over monolinguals in visual search tasks.Hernández et al. (2012) found that young adult Spanish–Catalan bilinguals deployed top-down attentional guidancemore efficiently than Spanish monolinguals in visual search.Prior to each search trial, their participants were shown a tilted

line embedded in a shape and were then required to locate thatsame line in an array. Critically, the tilted line was locatedeither in the cued shape (a benefit) or a different shape (a cost).Overall, bilinguals responded faster than monolinguals andshowed no effect of cueing. The authors suggested that bilin-guals rely more on top-down attentional guidance, and canbetter avoid distraction from irrelevant items.

Friesen and colleagues (2015) compared young adult bilin-guals and monolinguals in feature and conjunction searchtasks. In feature search, target shapes differed from distractorsby only one feature (e.g., color). In conjunction search, targetsdiffered by two features (e.g., color and shape; Treisman &Gelade, 1980). The authors also manipulated discriminabilitybymaking distractors more or less similar to targets in color. Abilingual advantage was only observed in the most difficultcondition (low discriminability, conjunction search); the au-thors suggested that bilinguals are more efficient at engagingand disengaging attention to visual objects.

Chabal, Schroeder, and Marian (2015) examined visualsearch performance between bilinguals and monolingualsusing an audiovisual task. Participants heard the name of atarget then proceeded to look for that item (e.g., hearing Bdog^and searching for a picture of a dog). During search, theyheard sounds that were consistent with the target (e.g.,barking), consistent with a distractor in the display, unrelatedto any item in the display, or they heard no sound. Theirfindings showed that bilinguals fixated targets faster thanmonolinguals, suggesting they had more efficient attentionalguidance. Additionally, visual search response times were cor-related with performance on EF tasks for the bilingual group,but not for the monolingual group. The authors concluded thatbilinguals use EF to facilitate relevant information and down-regulate distracting or irrelevant information.

Behavioral measures of visual search have indicated advan-tages for bilinguals, but the relative coarseness of reaction timeand accuracy measures leaves open the possibility that morenuanced conclusions may be drawn by using more fine grainedeyetracking measures. In particular, eyetracking may be useful inexamining potentially subtle differences between bilingual andmonolingual young adults. Although behavioral measures havesuggested a bilingual advantage in children and older adults (e.g.,Bialystok & Viswanathan, 2009; Emmorey et al., 2008), theresults of studies on young adults have been less consistent(e.g., Hilchey & Klein, 2011; Paap & Greenberg, 2013; Paap,Johnson, & Sawi, 2015; Ratiu & Azuma, 2015). For example,Paap and Greenberg examined whether a bilingual advantageexists in inhibition, monitoring, and task switching abilities usingmultiple executive function tasks, including an antisaccade task,Simon task, and color–shape switch task. However, the authorsfound no evidence of a bilingual advantage in any of these tasks.Paap and Greenberg argued that the executive function advan-tage attributed to bilingualism could be explained by other fac-tors, such as task-specific performance, or demographic factors

1696 Atten Percept Psychophys (2017) 79:1695–1725

(including age). Similarly, Ratiu and Azuma examined thebilingual advantage in WMC, but did not observe a bilingualadvantage in any task. In a recent review, Paap et al. (2015)argued that the bilingual advantage could reflect publication bias,differences in socioeconomic status, immigrant status, question-able statistics, and tasks that are not sensitive to individual differ-ences in domain-general processes.

These previous investigations have used the behavioral mea-sures of accuracy and response time, which may lack the sensi-tivity required to detect a bilingual advantage in young partici-pants who are at their cognitive peak (Bialystok, 2006; Costaet al., 2009; Kousaie & Phillips, 2012; Paap & Greenberg,2013). Eyetracking measurements permit more sensitive, real-time examination of cognitive processing during visual searchand can allow us to explore the purported bilingual advantagemore closely.

Prior studies using eyetracking to examine bilingual cognitiveadvantages have produced mixed findings. In an antisaccadetask, Bialystok, Craik, and Ryan (2006) found that bilingualsresponded faster than monolinguals when the task included akeypress, but the groups did not differ in their eye movements.The authors proposed that bilinguals had more efficient responseinitiation. In a related study, Singh and Mishra (2012, 2013)compared low- and high-proficiency Hindi–English bilinguals,measuring saccade latencies in an oculomotor version of theStroop task. Participants were required to fixate on coloredsquares that were consistent with cued colors but inconsistentwith cued directions (e.g., a downward red arrow, paired with atarget red square located above the cue). More proficient bilin-guals were faster at initiating correct saccades, suggesting thatbilingual proficiency may affect attention control.

In visual search, successful performance requires a person toefficiently guide attention to potential target objects and thenmake swift, accurate decisions about each inspected item (e.g.,Godwin, Walenchok, Houpt, Hout, & Goldinger, 2015).Previous findings suggested that bilinguals are more efficientthan monolinguals at finding target stimuli embedded amongdistractors (Friesen et al., 2015; Hernández et al., 2012). Thisvisual search advantage may reflect better attentional guidanceor faster response initiation (as was suggested by Hilchey &Klein, 2011), or a combination of both. The specific process(es)underlying the bilingual advantage shown in prior visual searchstudies cannot be determined, as overall response times (RTs)share contributions from both processes (see Hout &Goldinger, 2015; Hout, Walenchok, Goldinger, & Wolfe,2015). Friesen et al. (2015) recommended that BFuture researchshould employ eye-tracking techniques to investigate whether itis the time course of engaging and disengaging attention whenscanning the display that is more rapid for bilinguals or whetherbilinguals are better able to initiate a response once the target hasbeen found^ (p. 700).

The present experiments were designed to explore visualsearch differences between monolinguals and bilinguals using

behavioral data and participants’ eye movements. Each taskrequired participants to make careful discriminations to detecttarget items among similar distractors. In Experiment 1, par-ticipants searched for a target embedded among distractorsthat were dissimilar (feature search) or similar (conjunctionsearch). In Experiments 2 and 3, participants performed visualsearch while making speeded discriminations after locatingthe target, and mentally updating a constantly changing target.

Experiment 1

In Experiment 1, we examined bilingual and monolingual per-formance on feature and conjunction visual search tasks.Previous studies have reported that bilinguals outperform mono-linguals on visual search tasks that require the inhibition of irrel-evant or distracting stimuli (e.g., Costa et al., 2009; Emmoreyet al., 2008). In this experiment, participants searched for aLandolt C target embedded among Os and Landolt Cs of differ-ent orientations. Search difficulty was manipulated by varyingthe similarity of distractors to the target, both in shape and incolor shades. Previous studies documenting a bilingual searchadvantage used color stimuli (e.g., Friesen et al., 2015;Hernández et al., 2012). Thus, it is possible that bilinguals weremore efficient at locating targets because theywere better at usingcolors to guide search. To address this possibility, one conditionin our experiment contained all black stimuli. Additionally, par-ticipants completed working memory and fluid intelligence tasks(symmetry span task and Raven’s Advanced ProgressiveMatrices, respectively) to ensure that any possible differencesin visual search performance would not be attributable to othercognitive differences.

It was expected that performance would decline for all partic-ipants with increased search difficulty (i.e., higher similarityamong distractors and targets). If a bilingual search advantagearises frommore efficient attentional guidance, bilinguals shouldshow faster first fixation times to targets, relative to monolin-guals. If a bilingual advantage arises from more efficient re-sponse initiation, bilinguals should have faster decision times(latency from the first fixation to the keypress) than monolin-guals. If the advantage arises from a combination of these pro-cesses, then bilinguals should show faster overall search RTs(latency from trial onset to the keypress). Given that the partici-pants were young adults, any bilingual differences should bemost evident in the difficult conjunction trials (e.g., Friesenet al., 2015).

Method

Participants

All participants were recruited from Arizona State Universityundergraduate classes and received partial course credit for

Atten Percept Psychophys (2017) 79:1695–1725 1697

participation. Participants were recruited using a general state-ment regarding the description of the study and criteria forparticipation. Separate recruitment materials were created formonolinguals and bilinguals, and participants were not pro-vided information regarding the hypotheses until debriefing.Bilingual participants reported speaking English and one otherlanguage fluently and reported no history of memory, lan-guage, or neurological problems. The Ishihara color visiontest was used to determine color blindness (Ishihara, 1917).A modified version of the Language Experience andProficiency Questionnaire (LEAP-Q; Marian, Blumenfeld, &Kaushanskaya, 2007) was used to measure relative languagefluency for the bilingual participants (see Table 1). All partic-ipants gave informed consent, and all procedures were ap-proved by the Arizona State University Human SubjectsInstitutional Review Board.

Experiment 1 included 15 English monolingual speakers and15 bilingual participants. The bilinguals self-reported speakingEnglish and one of the following languages: Mandarin (6),Korean (3), other (6). The monolingual group had four females,a mean age of 19.7 years (SD = 2.0), andmean education of 13.5years (SD = 0.74). The bilingual group featured five females, amean age of 20.0 years (SD = 2.4), and mean education of 13.6years (SD = 0.90). The groups did not significantly differ in age,education, or maternal education (all ts < 1).1

Stimuli

In both the black and the color conditions, the target wasalways a Landolt C with a gap on the top, bottom, left, orright. The three levels of trial difficulty (easy, medium, diffi-cult) differed in the degrees of similarity among the targets anddistractors (e.g., Duncan & Humphreys, 1989).

Black condition All stimuli were black. The distractorsconsisted of circles and/or Landolt Cs with gaps at differentorientations than the target. In easy trials, the distractorsconsisted of 100% circles. In medium trials, the distractorswere primarily circles with four Cs in each search display(one per quadrant). In target-present trials, one of the Cs wasthe target. In difficult trials, the distractors were all Cs thatmismatched the target orientation.

Color condition The distractors were Landolt Cs that mis-matched the target in gap orientation, color, or both. Colorswere selected from 16 possible colors that composed aBwheel^ of hues, wherein each color was equally differentfrom its neighbors in color space (Stroud, Menneer, Cave, &

Donnelly, 2012; see Fig. 7 in Appendix H). Target colors wererandomly selected from four possible (equidistant) locationson the wheel, roughly corresponding to Borange,^ Bgreen,^Bblue,^ and Bpink.^ In the easy condition, no distractorsmatched the target color, making it similar to a Bpop-out^search task (Treisman & Gelade, 1980). In the medium con-dition, distractors were equally sampled from all four targetcolors and all four orientations. In the difficult condition,distractor colors were drawn from the same categories as tar-gets (e.g., Boranges^). One-third of the distractors exactlymatched the target color, and the remaining distractors dif-fered by only one step in color space. Distractor orientationswere randomly sampled with the constraint that the target-colored distractors had a different orientation than the target.

Procedure

All visual search experiments were presented stimuli using E-Prime 2.0 software (Schneider, Eschman, & Zuccolotto, 2012).Data were collected using a Dell Optiplex 755 PC. The displaywas a 21-in. NEC FE2111SB CRT monitor (20 in. viewable),with resolution set to 1,280 × 1,024 and a 75-Hz refresh rate. Eyemovements were recorded using a desktop-mounted EyeLink1000 eyetracker (SR Research Ltd., Mississauga, Ontario,Canada). Temporal resolution was 500 Hz, and spatial resolutionwas 0.01°. Participantswere initially calibrated to ensure accuratetracking and used a chin rest during all search trials. Periodic driftcorrection and recalibrationswere used to ensure accurate record-ing of gaze position. The Landolt C stimuli subtended approxi-mately 1° × 1° (centered).

Symmetry span task (Unsworth, Heitz, Schrock, & Engle,2005) Participants were shown black-and-white images and re-ported whether each was symmetrical around its vertical axis. Toindicate their response, participants clicked on the image with acomputer mouse, which triggered YES and NO options to ap-pear. Images appeared for 4,000 ms or until the mouse click.After entering a response, participants saw a 4 × 4 matrix withone square shaded red for 1,000 ms. Following the matrix, an-other image appeared for symmetry judgment. At a recallprompt, participants indicated the order and location of the redsquares by clicking on squares in a blank grid, then receivedaccuracy feedback. Sets contained two to six symmetry–matrixpairs with two trials per span length (i.e., number of correctlyrecalled shaded squares), presented in random order.

Raven’s Advanced Progressive Matrices All participantscompleted an abbreviated version of Raven’s AdvancedProgressive Matrices (RAPM; Raven, Raven, & Court,1998), a measure of general fluid intelligence. In each trial,participants saw displays of 3 × 3 matrices of geometric patternswith the bottom right pattern missing. Participants selected apattern to complete the series from a set of eight possibilities.

1 Maternal education ranged from 1 to 8 (1 = junior high/middle school, 2 =some high school, 3 = high school diploma, 4 = some college, 5 = associate’sdegree, 6 = bachelor’s degree, 7 = master’s degree, 8 = doctorate/professionaldegree).


The task continued until 18 problems were completed (the trialsprogressively increased in difficulty) or 10 min had elapsed.

Visual search After completing 12 practice trials, each partici-pant completed 54 black trials, followed by three blocks of 36color trials. In all conditions, each trial contained an initial cuescreen showing the target Landolt C (randomly selected in eachtrial); the cue remained visible until the participant pressed thespace bar to begin the search. A central fixation cross wasdisplayed until the participant had looked directly at it for 500ms, after which the search display appeared. The displaycontained 16, 20, or 24 images. Targets appeared in half of thetrials in random locations. Participants were instructed to pressthe space bar when they had located the target or decided that thetarget was not present, with a maximum of 15 s to complete each

trial. After they had pressed the space bar, the search displaydisappeared. Participants indicated target presence or absenceby pressing the Bf^ or Bj^ keys, respectively, on a standard key-board. Feedback was given after each trial (see Fig. 1 for theprogression of events per trial). After completing the visualsearch experiment, participants completed the symmetry spanand RAPM tasks, in counterbalanced orders.

Results

In all experiments, standard visual search effects were observed.RTs were slower in the target-absent than in the target-presenttrials (Exp. 1), and RTs were slower when the distractors weremore similar to the target (Exps. 1–3). This confirms that oursearch difficulty manipulations were effective. For brevity, we

Table 1 Language profile forbilingual participants in allexperiments

Self-Ratings for Language 1 Self-Ratings for Language 2

Experiment 1

Daily use 64.33% (15.91) Daily use 32.67% (15.91)

Daily reading 71.43% (29.92) Daily reading 25.71% (24.14)

Age of acquisition 0.33 (0.90) Age of acquisition 7.40 (4.39)

Age fluent 6.07 (3.65) Age fluent 12.43 (6.24)

Proficiencya Proficiencya

Speaking 9.80 (0.41) Speaking 7.00 (1.57)

Understanding 9.73 (0.46) Understanding 7.66 (1.80)

Reading 9.60 (0.63) Reading 5.93 (2.40)

Experiment 2








Reading 9.61 (0.70) Reading 7.56 (1.92)

Experiment 3








Reading 9.62 (0.72) Reading 7.00 (2.51)

ªSelf-ratings for proficiency questions are based on a 10-point scale.

Note: Standard deviations are in parentheses.


Fig. 1 Progression of trial events in Experiment 1


focus our reporting on themain effects and interactions involvingspeaker group, since these were the analyses of interest. The fullstatistics for RTs are reported in Table 2 and Appendix Table 3.The same analyseswere conducted on accuracy. For accuracy, nosignificant main effects of speaker group emerged for any mea-sure (Exps. 1–3), nor reliable interactions between speaker groupand the other factors. Additionally, performance was at 94% orhigher in every experiment, raising concerns about ceiling effectsand making the analyses difficult to interpret. Thus, we do notreport the accuracy data.

Normative measures

Therewas no difference between bilinguals andmonolinguals onRAPM [t(29) = 1.13, p = .269]. Bilinguals performedmarginallybetter than monolinguals on the symmetry span task [t(29) =1.89, p = .068].

Visual search

Overall search RTs, first fixation times, and decision times areshown in Table 2. A 2 (Trial Type: absent or present) × 3(Search Difficulty: easy, medium, or difficult) × 2 (SpeakerGroup: monolingual or bilingual) mixed-model analysis ofvariance (ANOVA) was conducted on the mean correct RTs.For first fixation and decision times, a 3 (Search Difficulty:easy, medium, or difficult) × 2 (Speaker Group: monolingualor bilingual) mixed-model ANOVAwas conducted on target-present trials only (see Appendix Table 3 for the main effectsand interactions). All post-hoc pairwise comparisons were

evaluated using a Bonferroni-corrected alpha of .017 for mul-tiple comparisons. All ANOVA results, including the effectsizes, are listed in Appendix Table 3. Individual RTs acrossall conditions (Exps. 1–3) are shown in Appendix I, Figs. 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18 and 19.

Overall search RT

The main effect of speaker group was not reliable in eithercolor condition. No other interactions were reliable.2

First fixation times

In both color conditions, only the main effect of search diffi-culty was significant, with no main effect or interactions in-volving speaker group.3

Table 2 Mean search times (in milliseconds) for target-present trials in Experiment 1

Black Color

Easy Medium Difficult Easy Medium Difficult

Overall Search

Bilingual 1,715.50 (422.25) 2,090.12 (668.14) 2,881.06 (750.37) 995.37 (210.98) 1,797.07 (393.54) 2,512.67 (637.29)

[1,466.34, 1,964.66] [1,751.20, 2,429.03] [2,443.07, 3,319.05] [875.30, 1,115.44] [1,608.08, 1,986.05] [2,192.19, 2,833.16]

Monolingual 1,790.30 (515.32) 2,138.51 (612.24) 3,281.11 (899.18) 967.17 (241.99) 1,750.01 (316.98) 2,517.84 (572.91)

[1,541.14, 2,039.45] [1,799.60, 2,477.43] [2,843.11, 3,719.10] [847.11, 1,087.24] [1,561.03, 1,938.99] [2,197.35, 2,838.33]

First Fixations

Bilingual 1,105.91 (333.46) 1,478.58 (422.30) 2,360.47 (658.48) 507.71 (106.96) 1,077.66 (247.02) 1,773.77 (478.94)

[932.12, 1,279.69] [1,267.88, 1,689.27] [2,012.33, 2,708.62] [453.78, 561.65] [963.96, 1,191.35] [1,561.47, 1,986.07]

Monolingual 1,225.73 (323.62) 1,469.54 (372.91) 2,307.18 (658.01) 466.07 (96.74) 1,107.51 (177.21) 1,630.73 (304.70)

[1,051.95, 1,399.51] [1,258.85, 1,680.24] [1,959.04, 2,655.32] [412.14, 520.01] [993.81, 1,221.20] [1,418.43, 1,843.02]

Decision Times

Bilingual 687.94 (334.46) 758.28 (422.88) 795.95 (352.22) 506.65 (174.65) 737.15 (254.99) 909.09 (294.91)

[514.57, 861.30] [552.35, 964.20] [546.01, 1,045.89] [408.89, 604.43] [608.59, 865.71] [699.90, 1,118.29]

Monolingual 670.24 (320.97) 735.03 (352.34) 1,037.44 (567.96) 510.45 (181.59) 689.88 (213.60) 1,017.40 (447.10)

[496.87, 843.60] [529.10, 940.95] [787.50, 1,287.38] [415.99, 604.90] [565.68, 814.08] [815.30, 1,219.50]

Standard deviations are in parentheses; 95% confidence intervals are shown in brackets.

2 Set size was sampled in equal proportions across all conditions. There wereno reliable Set Size × Speaker Group interactions for overall search RTs, firstfixation times, or decision times. In post-hoc comparisons, there were noreliable differences between bilinguals and monolinguals for any set size. Inthe interest of brevity, we avoid reporting set size effects or interactions. Due tothe high number of conditions in Experiment 1 (trial type, search difficulty,speaker group, and set size), there were too few trials per condition for a 2.5-SD cutoff criterion to be applied.Due to occasional missing eye movement data, the overall search RTs do not

equal the sum of the first fixations times and decision times.3 In addition to first fixation times, oculomotor control was also measuredusing scan path ratios, which are the summed amplitudes of all saccades (indegrees of visual angle) prior to target fixation, divided by the shortest possibledistance between the central fixation and the target (e.g., Hout & Goldinger,2015). The analyses revealed no reliable scan path ratio differences betweenspeaker groups in any experiment.


Decision times

As with first fixation times, the main effect of speaker groupwas not significant. The Search Difficulty × Speaker Groupinteraction was marginal (p = .055) in the black condition(slightly favoring the bilingual group), and was null in thecolor condition.

Bayes analysis

We computed scaled Jeffrey–Zellner–Siow (JZS) Bayes factorvalues for speaker group across the three experiments (seeAppendix Table 9). This analysis shows moderately strongevidence in favor of the null hypothesis (about 3:1) in nearlyall comparisons, and a monolingual advantage in onecomparison.

Language balance

To assess whether bilingual language experience predictedvisual search performance, language balance (calculated asratio of average proficiency in the second and first language)was used as a predictor in simple linear regression analyses.Language balance did not predict overall search RTs, firstfixation times, or decision times in either color condition atany level of search difficulty (all ps > .05).

Discussion

In Experiment 1, bilinguals and monolinguals performed visualsearch under varying degrees of difficulty. The findings wereconsistent with previous studies with regard to search difficulty(e.g., Duncan & Humphreys, 1989), but there were no RT dif-ferences between bilinguals and monolinguals in any condition.Additionally, search RTs did not vary as a function of languagebalance in bilinguals. These results contrast with previous find-ings of an overall bilingual advantage in visual search (e.g.,Friesen et al., 2015; Hernández et al., 2012). There was also noconsistent evidence of a bilingual advantage in the eye move-ment data: Search guidance, as measured by first fixation times,was equivalent for both groups.

Interestingly, bilinguals had marginally faster decision timesthan monolinguals in the most difficult black condition, but nogroup differences were observed in the color condition. This mayindicate that a bilingual advantage in visual search occurs at thedecision level, when the target template held in memory ismatched to the visual stimulus. Bialystok, Craik, and Ruocco(2006) found that bilinguals were faster than monolinguals onan antisaccade task when the participants were required to re-spond using a keypress. The authors argued that bilingualismmay affect the symbolic mapping between a visual stimulusand the appropriate response. This marginal difference may bemore robust when decisions are made more difficult.

Experiment 2

The marginal group difference in decision times observed inExperiment 1 suggests that, if there is a bilingual advantage invisual search, it may occur at the decision-making stage, ratherthan during attentional guidance. To examine this possible ad-vantage more closely, we modified the task to increase the diffi-culty of the decision. Participants performed visual search, duringwhich they reported the color or shape of geometric figures em-bedded within target Landolt Cs. In some blocks, participantsonly reported the color or shape of the embedded geometricfigure. In other blocks, they alternated between color and shapedecisions.

Previous researchers have reported bilingual advantages insimilar switching tasks. Prior and MacWhinney (2010) com-pared bilinguals and monolinguals in a switching task whereinparticipants were shown red or green circles and triangles, andwere asked to report either the color or shape. Performance wasmeasured by examining switching and mixing costs in RTs.Switching costswere calculated by comparing switch and repeattrials in a switching-only condition. BSwitch^ trials were definedas a Bshape^ decision following a Bcolor^ decision, or vice versa.Mixing costs were calculated by comparing repeat trials in theswitching condition to repeat trials in color-only or shape-onlyconditions. The authors found that bilinguals showed reducedswitching costs, relative to monolinguals, but equivalent mixingcosts. They suggested that lifelong bilingual experience contrib-uted to task switching advantages. Additionally, Prior andGollan(2011) observed that bilinguals who reported more frequent lan-guage switching showed reduced switching costs, as comparedboth to monolinguals and to bilinguals who reported less fre-quent language switching. The authors proposed that daily lan-guage habits may shape general cognitive mechanisms that playa role in nonverbal tasks (see also Soveri, Rodriguez-Fornells, &Laine, 2011). If bilinguals have an advantage over monolingualsin both task switching and decision efficiency under difficultvisual search conditions, they should show faster decision times,particularly in the switching condition.

Method

Participants

Nineteen English monolingual speakers and 18 bilingualspeakers participated in Experiment 2. No volunteers had par-ticipated in Experiment 1. Recruitment procedures were identicalto Experiment 1. Bilingual speakers reported speaking Englishand one the following languages: Spanish (9), French (2),Korean (2), Mandarin (1), Arabic (1), Navajo, (1), Serbian (1),and Vietnamese (1). The monolingual group had ten females, amean age of 18.6 years (SD = 0.90) and mean education of 13.3years (SD = 0.56). The bilingual group had 11 females, a meanage of 19.1 years (SD = 1.74) and mean education of 13.2 years


(SD = 0.57). The groups did not differ in age, education, ormaternal education (all ts < 1.18).

Stimuli

The targets were Landolt Cs with gaps on the top, bottom, left, orright. All targets and distractors were black. Embedded withineach Landolt C was a triangle or square shape, which was eithersolid black (filled) or an outline of the shape (unfilled). Stimuliwere presented in the easy (100% circle distractors), medium(50% circle distractors, 50% Landolt C distractors), and difficult(100% Landolt C distractors) conditions.

Procedure

Each participant was familiarized with the shape and colorjudgments prior to the visual search trials. In each practicetrial, either the word Bshape^ or Bcolor^ was shown, alongwith a reminder of the response keys, followed by a 1,000-ms fixation cross and a single Landolt C in the center of thescreen, containing an embedded shape. In shape trials, theparticipant quickly judged whether the shape was a triangleor a square by pressing the Ba^ or Bd^ keys, respectively, whileignoring the color of the shape. Responses had to be madewithin 5 s or the trial was terminated. In color trials, the par-ticipant judged whether the embedded shape was unfilled orfilled by pressing the Bj^ or Bl^ keys, respectively, while ig-noring the particular shape. Participants rested their index andmiddle fingers of each hand on these keys throughout theexperiment. The practice session consisted of 20 color judg-ment trials, 20 shape judgment trials, and a block of 40 switchtrials, in which color and shape judgments were randomlyintermixed. The practice switching block was repeated if theparticipant did not achieve 80% accuracy.

The experimental trials were similar to the practice trials,with the addition of a visual search component (see Fig. 2 for aschematic trial). At the onset of each trial, the participant wasshown the target Landolt C without an embedded shape, alongwith the word Bshape^ or Bcolor,^ indicating the judgmentrequired for that trial. The subsequent visual search display(preceded by a 500-ms fixation cross) contained 24 stimuli,each with an embedded shape. One of the shapes was thetarget. Participants were instructed to quickly locate the targetand make the appropriate Bshape^ or Bcolor^ judgment. Thetrial terminated when any response key was pressed (or when15 s had elapsed). After completing 24 practice trials, partic-ipants completed three blocks each of color-only, shape-only,and switch trials, and each block contained either easy, medium,or difficult trials. Each single-task block (color or shape)consisted of 20 trials, whereas the switch blocks consisted of40 trials. The eyetracking apparatus was the same as inExperiment 1, and the same measurements were collected.After completing the search portion of the experiment,

participants completed symmetry span and RAPM incounterbalanced order across participants.

Results

We again focus on the main effects and interactions involvingspeaker group, since these were the analyses of interest.

Normative measures

There were no reliable group differences between bilingualsand monolinguals on either the symmetry span task or RAPM(both ts < 1.3).

Visual search

RTs slower than 2.5 SDs from individual participantmeans were removed from analyses (2.7% of the data).Another 2.5-SD cutoff was used to remove outliers fromthe first fixation times and decision times (2.4% of thedata). A 3 (Decision Block: color, shape, or switch) × 3(Search Difficulty: easy, medium, or difficult) × 2(Speaker Group: monolingual or bilingual) mixedANOVA was conducted on the mean correct RTs (seeAppendix Table 4 for all ANOVA results, includingeffect sizes). All post-hoc pairwise comparisons wereevaluated using a Bonferroni-corrected alpha of .017 forsimultaneous comparisons. Figure 3 shows all the visualsearch results, with overall RTs in panel A, first fixationtimes in panel B, and decision times in panel C (see alsoAppendix Table 7).

Mixing costs and switching costs were also analyzed.Switching costs reflect the difference between switch trials(from shape to color, or vice versa) and repeat trials in theswitch condition. Mixing costs reflect the difference betweenrepeat trials in the switch condition and responses in thesingle-decision conditions (see Prior & Gollan, 2011; Prior& MacWhinney, 2010). Mixing costs were calculated bysubtracting the average RT for repeat trials in the single-decision conditions (color and shape) from the average RTfor repeat trials in the switch condition. Costs were analyzedusing a 2 (Cost Type: switching or mixing) × 3 (SearchDifficulty: easy, medium, or difficult) × 2 (Speaker Group:monolingual or bilingual) mixed ANOVA.

Overall search RT

The main effect of decision block was reliable: RTs in theswitch condition were slower than RTs in the color [t(36) =3.25, p = .003] and shape [t(36) = 2.72, p = .010] conditions.The main effect of speaker group was null. The three-wayinteraction was significant (p = .038); however, none of the


Fig. 2 Progression of trial events in Experiment 2


post-hoc comparisons were reliable. No other interactionswere reliable.4

Figure 4 shows switching costs (panel A1) and mixingcosts (panel A2) in overall search RTs. The main effect of costtype was reliable [F(1, 35) = 4.56, p = .040, ηp

2 = .044]:Mixing costs (M = 207 ms) were greater than switching costs(M = −34 ms). The main effect of speaker group was notsignificant (F < 1), and the three-way interaction was marginal[F(2, 70) = 3.12, p = .051, ηp

2 = .082]. Monolinguals hadsmaller switching costs than bilinguals in the medium anddifficult search conditions, but these differences were not re-liable. Bilinguals had marginally smaller mixing costs in the

difficult search condition [t(35) = 2.44, p = .020]. No otherinteractions were significant.


The main effect of speaker group was not reliable (seeFig. 3B), nor were any interactions. For the cost analysis, themain effect of cost type was marginal [F(1, 35) = 3.92, p =.056, ηp

2 = .101], with mixing costs (M = 69ms) being slightlygreater than switching costs (M = −114 ms; see Fig. 4, panelsB2 and B1, respectively). No other effects or interactions werereliable (all Fs < 1.79).5

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Fig. 3 Results from Experiment 2. (A) Mean overall search RTs. (B) Mean first fixation times. (C) Mean decision times. Error bars show ±1 SEM

4 An additional 40 bilinguals and 41 monolinguals completed the behavioralportion of the experiment. For these participants, we found a significant maineffect of decision block [F(2, 158) = 45.89, p < .001, ηp

2 = .367] on overallsearch RTs. There was also a significant three-way Condition × SearchDifficulty × Speaker Group interaction [F(4, 316) = 2.53, p = .041, ηp

2 =.031], but no post-hoc comparisons were reliable. In the cost analysis, theSearch Difficulty × Speaker Group interaction was significant [F(2, 158) =3.27, p = .041, ηp

2 = .040]; however, no post-hoc comparisons were reliable.No other main effects or interactions were reliable.

5 During the initial portion of the visual search task, reflected by the firstfixation times, participants are scanning the screen for a target item. It isunlikely that the switching or mixing costs affected this part of the task.Thus, these graphs should be interpreted with caution. The switching andmixing costs are most accurately reflected in decision times.


Decision times

The results from the decision time analyses are depicted inFig. 3C. The main effect of decision block was reliable, withslower decision times in the switch than in the shape condition[t(36) = 5.27, p < .001], as well as slower decision times in thecolor than in the shape condition [t(36) = 4.56, p < .001].Decision times were not significantly different in the color andswitch conditions (t < 1.55). The main effect of speaker groupwas null, and no interactions were reliable. In the cost analysis(shown in Fig. 4C), no main effects or interactions weresignificant.

Language balance

As in Experiment 1, linear regression analyses were conductedfor the bilingual group using language balance as a predictorvariable. Language balance was not a reliable predictor of overallsearch RTs in any condition (all ps > .05), although it was amarginally significant predictor of first fixation times in theswitching condition under difficult visual search (β = −.468)[t(17) = −2.12, p = .050, R2Adj = .170]. Language balance wasa reliable predictor of decision times in the color condition undermedium search difficulty (β = −.505) [t(17) = −2.34, p = .032,R2Adj = .209], and in the shape condition under difficult search (β

= −.494) [t(17) = −2.27, p = .037, R2Adj = .197], but it did notpredict switching or mixing costs for any measure (all ps > .10).

Discussion

As expected, search performance decreased as difficulty in-creased, particularly under task switching conditions. However,no reliable visual search differences emerged between bilingualsandmonolinguals in the behavioral or eyetrackingmeasures. Themarginal group difference in decision times observed inExperiment 1 was not replicated in Experiment 2. Indeed, bilin-guals showed a slight disadvantage in decision times in the dif-ficult color task condition. Overall, the RT and eye movementresults argue against a bilingual advantage in task switching dur-ing visual search (in particular decision times). Only one impor-tant trend was observed in the proficiency analyses: Balancedbilinguals, as compared to bilinguals who use one language pre-dominantly, had faster decision times in two measures (in themedium difficulty color condition and the difficult shape condi-tion). However, this trend was not consistent across conditions.

Previous studies have reported bilingual advantages inswitching costs (e.g., Prior & Gollan, 2011; Prior &MacWhinney, 2010). In Experiment 2 we observed a marginalbilingual advantage, but only in mixing costs and overall searchRTs, not in decision times or first fixation times. Additionally,

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Fig. 4 Results from Experiment 2. (A) Overall search RTs: Switching costs (A1) and mixing costs (A2). (B) First fixation times: Switching costs (B1)and mixing costs (B2). (C) Decision times: Switching costs (C1) and mixing costs (C2). Error bars show ±1 SEM


there was a bilingual disadvantage in switching costs. Given theinconsistent effects across measures, these results do not supporta bilingual advantage in task switching.

Experiment 3

Experiments 1 and 2 provided no clear evidence of a bilingualadvantage in attentional guidance or decision-making process-es. Bilinguals were largely indistinguishable from monolin-guals in their visual search performance, whether they wererequired to inhibit irrelevant information (Exp. 1) or to switchattentional sets (Exp. 2). However, bilinguals might still dem-onstrate a cognitive advantage over monolinguals in their abil-ity to update and/or continuously monitor information held inworking memory. Experiment 3 was conducted to investigatethis possibility.

Previous studies have suggested that bilinguals show dual-task advantages (e.g., Bialystok, Craik, & Ruocco, 2006). InExperiment 3, we investigated whether bilinguals and mono-linguals differed in the monitoring of information and theupdating of items held in working memory within the contextof a visual search task. Bialystok, Craik, and Ruocco investi-gated updating and monitoring using a dual-modality taskwith both auditory and visual stimuli. Their participants simul-taneously sorted auditory and visual items into categories (let-ters/numbers and animals/musical instruments), using akeypress for visual items and verbal responding for auditoryitems. Bilinguals correctly sorted more items than monolin-guals, suggesting superior updating and monitoring ability.However, other researchers have failed to observe a bilingualadvantage in dual-task performance. Moradzadeh,Blumenthal, and Wiseheart (2015) investigated bilinguals’dual-task performance on a Krantz (2007) task and a dual n-back task. In the Krantz task, participants tracked a movingdot while simultaneously attending to a series of flashing let-ters. In the dual n-back task, participants simultaneously re-ported whether a visual stimulus (e.g., colored square) and anauditory stimulus (e.g., digit) matched a previously presentedvisual or auditory stimulus. Moradzadeh et al. failed to ob-serve a bilingual advantage in either task.

Following these studies, the participants in Experiment 3performed a dual task within the visual search paradigm,which required the target stimuli to be continuously updated.Participants mentally rotated a target Landolt C for the searchtask, remembered an abstract shape for a memory task, orsimultaneously performed both tasks. This design enabled usto investigate whether a bilingual advantage might take theform of better updating of memorial representations, betterability to hold an image in memory, or a combination of both.Previous results (e.g., Bialystok, Craik, & Ruocco, 2006) sug-gested that a bilingual advantage in updating should be

observed in the most demanding condition (i.e., dualmonitoring).

Method

Participants

Twenty-four new English monolingual speakers and twenty-nine new bilinguals participated in the experiment. The re-cruitment procedures were identical to those of Experiment1. Bilingual speakers reported speaking English and one ofthe following languages: Spanish (11), Mandarin (7), Hindi(2), or other (9). The monolingual group featured 16 females,a mean age of 18.75 years (SD = 0.79), and mean education of13.7 years (SD = 0.82). The bilingual group featured 18 fe-males, a mean age of 20.76 years (SD = 3.03), and meaneducation of 14.0 years (SD = 2.76). The groups did not differin either education or maternal education (both ts < 1.65), butthe bilinguals were significantly older than the monolinguals[t(51) = 3.15, p = .003].

Stimuli

Targets consisted of Landolt Cs with gaps on the top, bottom,left, or right. All targets and distractors were black. Novelshape (polygon) stimuli were taken from Tat and Azuma(2016), with each subtending approximately 2° × 2° (cen-tered). We created three stimulus conditions: easy (50% ofthe distractors were circles and 50% were Landolt Cs), medi-um (25% circles and 75% Landolt Cs), and difficult (100%Landolt Cs).

Procedure

The visual search task was administered across four condi-tions: (1) only visual search, (2) visual search with updating,(3) visual search with secondary memory task, and (4) visualsearch with updating and secondary memory task.

Updating task The updating component required participantsto mentally update a target Landolt C over successive trials. Intrial n, the target C was shown. In trial n+1, the target wasremoved, and participants had to mentally rotate the targetcounterclockwise 90 degrees from the previous trial. Afterincorrect search trials, participants were reminded of the cur-rent target (these trials were discarded from the analysis).

Secondary memory load In the secondary-load component,participants remembered a polygon shown prior to each visualsearch trial. After completing the search task, a final screenwith four polygon alternatives was displayed, and participantsselected the correct polygon by pressing the Bd,^ Bf,^ Bj,^ or


Bk^ key. The final screen was shown until the participantresponded (or until 10 s had elapsed).

In all conditions, an initial screen depicted a polygon priorto search, and a final screen depicted four polygons after thesearch. In conditions without the secondary task, participantswere told simply to ignore the polygons. The initial screenwasshown for a maximum of 10 s or until the space bar waspressed. Following a gaze-contingent 500-ms fixation cross,the participants were shown the Landolt C target cue until theypressed the space bar to begin the search. Note that in condi-tions that included the updating task, the target cue was notdisplayed after correct updating trials. In all search trials therewere 24 items, including the target, which was presented in arandom location. The search display was terminated when theparticipants pressed the space bar (or after 15 s had elapsed).After the space bar was pressed, the stimuli were replaced bynumbers for 1,000 ms. The participants indicated the targetlocation by selecting its number from two alternatives shownin a subsequent probe screen. After search feedback was pre-sented, the final screen of polygons was displayed (for condi-tions without the secondary task, this screen was displayed for2,000 ms). See Fig. 5 for a sample trial progression.

Participants completed one block apiece of easy, medium,and difficult trials across each of the four task conditions, for atotal of 12 randomly ordered blocks with 16 trials each.Participants also completed six practice trials for each condi-tion, for a total of 24 practice trials. Each participant wasrequired to attain 80% accuracy in each practice condition,or the condition would restart until this criterion was satisfied.After completing the search tasks, participants completed thesymmetry span and RAPM tasks, with the ordercounterbalanced across participants.

Results

We again focus on the main effects and interactions involvingspeaker group, since these were the analyses of interest.

Normative measures

We found no reliable group differences between bilingualsand monolinguals on either the symmetry span task orRAPM (both ts < 1).

Visual search

Search RTs slower than 2.5 SDs from the individual participantmeans were removed from the analyses (2.9% of the data).Another 2.5-SD cutoff was used to remove outliers from the firstfixation times and decision times (2.8% of the data). A 4(Updating Condition: control, updated search, secondary load,or dual task) × 3 (Search Difficulty: easy, medium, or difficult)× 2 (Speaker Group: monolingual or bilingual) mixed ANOVA

was conducted on the mean correct RTs (see Appendix Table 5for all ANOVA results, including effect sizes). Post-hoc pairwisecomparisons were evaluated using Bonferroni-corrected alphasof .017 or .01, for three or six simultaneous comparisons, respec-tively. Figure 6 shows all visual search results, with overall RTsin panel A, first fixation times in panel B, and decision times inpanel C (see also Appendix Table 8).

Overall search RT

The main effect of updating condition was significant: RTs inthe dual-task condition were slower than those in the control[t(50) = 7.05], updated search [t(52) = 4.50], and secondary-load [t(49) = 5.88] conditions (all ps < .001). Additionally, theupdated-search condition RTs were slower than both the con-trol condition RTs [t(51) = 3.77, p < .001] and the secondary-load condition RTs [t(59) = 2.90, p = .006]. Although the maineffect of speaker group was not significant, there was a signif-icant Updating Condition × Speaker Group interaction (seeFig. 6A). Bilinguals were slower than monolinguals in thedual-task condition (4,802 vs. 4,338 ms) and in the updated-search condition (4,411 vs. 3,720 ms), but were slightly fasterin the control condition (3,275 vs. 3,482 ms). The groups werestatistically equivalent in the secondary-load condition (t < 1).The Search Difficulty × Speaker Group interaction was sig-nificant, but post-hoc comparisons were not statistically reli-able. No other interactions were reliable.


There was a significant main effect of updating condition:First fixations to targets were slowest in the dual-task condi-tion, relative to the other three conditions [all ts(51) > 3.90, p <.001]. We observed no reliable effect of speaker group, norany reliable interactions (see Fig. 6B).

Decision times

The main effect of updating condition was significant, withslower decision times in the dual-task condition, relative to allothers (all ts > 3.2, p < .01). Additionally, updated-search condi-tion decision times were slower than control and secondary-loadcondition decision times [t(53) = 5.04 and 5.44, respectively, ps <.001]. The main effect of speaker group was robust: Bilingualshad significantly slower decision times than monolinguals. Thethree-way interaction was also reliable, with differences betweenthe groups varying across conditions and difficulty levels (seeFig. 6C).

Secondary task performance

In the secondary-load and dual-task conditions, bilinguals andmonolinguals did not differ in secondary-task accuracy (both ts


Fig. 5 Progression of trial events in Experiment 3, depicting the dual-task condition


< 1). Accuracy for the polygon memory task also did not differbetween the secondary-load and dual-task conditions (t < 1).

Language balance

As in Experiments 1 and 2, linear regression analyses were con-ducted for the bilingual group using language balance as a pre-dictor variable. Language balance significantly predicted overallsearch RTs in the control condition under easy search (β = .459)[t(28) = 2.68, p = .012, R2Adj = .181], as well as first fixationtimes in the medium difficulty condition (β = .393) [t(27) = 2.18,p = .038, R2Adj = .122]. Additionally, language balance was areliable predictor of decision times in the control condition undereasy search (β = −.387) [t(28) = −2.18, p = .038, R2Adj = .118].No other regression analyses were reliable.

Discussion

As expected, visual search was slower with increased taskdifficulty. Search RTs confirmed that the dual-task condition

was most difficult, followed by updated search, secondaryload, and control. As in Experiments 1 and 2, no bilingualadvantage in search RTs was observed for any condition. Itwas hypothesized that any bilingual dual-task advantageshould be most evident in the conditions with the greatestcognitive demands (e.g., the dual-task/difficult condition).However, the bilingual and monolingual groups performedequivalently in the easy and difficult conditions, and bilin-guals were marginally slower than monolinguals in the medi-um condition. Additionally, when participants had to mentallyupdate targets, bilinguals were generally slower than mono-linguals, a difference reflected in increased decision times.Eye movement analyses revealed no evidence of a bilingualadvantage in search guidance (first fixation time) or responseefficiency (decision time). Indeed, the most reliable groupdifference was a bilingual disadvantage in decision times.These findings argue against a bilingual advantage in visualsearch and dual-task performance, and are inconsistent withprevious reports of a bilingual advantage, particularly underconditions of highmonitoring (e.g., Costa et al., 2009), but are

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Fig. 6 Results from Experiment 3. (A) Mean overall search RTs. (B) Mean first fixation times. (C) Mean decision times. Error bars represent ±1 SEM


consistent with the findings of Moradzadeh et al. (2015), whoalso failed to observe a bilingual dual-task advantage.

General discussion

The present experiments used nonverbal visual search paradigmsto explore possible bilingual advantages in visual search, acrossdifferent levels of search difficulty and under various cognitivedemands. Previous investigations of the purported bilingual ad-vantage in visual search have been inconsistent; however, thesestudies mainly employed relatively coarse-grained dependentmeasures such as RT and accuracy. Such measures may not besufficiently sensitive to reveal subtle group differences. We ex-amined fine-grained eyetracking measures, which allowed us toassess whether bilinguals and monolinguals differed in attention-al guidance or in perceptual decision-making. Each experimentrecruited a distinct set of cognitive demands in order to broadlyinvestigate the conditions under which a bilingual advantagemay exist: Experiment 1 was conducted to investigate whetherbilinguals exhibit an enhanced ability to inhibit irrelevant visualinformation, by presenting feature and conjunction search tasksacross different difficulty levels. Experiment 2 examinedwhetherbilingualism confers a benefit in the ability to switch tasks whenmaking decisions, by requiring participants to alternate betweendifferent attentional sets throughout the visual search session.Experiment 3 was conducted to test for a potential bilingualadvantage in the ability to continuously monitor and update in-formation, by requiring participants to mentally rotate their inter-nal visual target templates while simultaneously maintaining anunrelated abstract image in memory.

Across all three experiments, there was no clear evidenceof a bilingual advantage in visual search. Our eye movementanalyses revealed no bilingual advantage in measures ofsearch guidance (i.e., first fixation times). Although bilingualsshowed a slight benefit over monolinguals in task switchingability in one condition of Experiment 2 (i.e., reduced costs inBrepeat^ trials that were intermixed with Bswitch^ trials), thisfinding is inconsistent with previous studies: Previous re-search has shown a bilingual advantage in task switching costs(i.e., the cost of switching types of decisions in consecutivetrials), but not in mixing costs (Prior & MacWhinney, 2010).Prior and MacWhinney suggested that mixing costs are asso-ciated with sustained activation of goal maintenance, which isrequired when potential responses compete with each otherand is associated with updating of mental representations(e.g., Miyake et al., 2000). If the slight bilingual advantagein mixing costs observed in the present study reflected bettergoal maintenance, this same advantage should have arisen inExperiment 3, which tested the ability to continuously main-tain and update relevant visual information. Given that nobilingual advantage was obtained in Experiment 3, the findingof reduced mixing costs for bilinguals was likely more

reflective of task-specific differences between groups, ratherthan differences in goal maintenance and updating ability.

Notably, although our bilingual sample was sufficiently rep-resentative, we observed no clear bilingual advantages, despiteusing tasks designed to place varying demands on executivefunction and working memory. Our sample was comparable tobilingual samples from similar studies (e.g., Chabal et al., 2015;Friesen et al., 2015; Hernández et al., 2012). Participants alsoreported acquiring both languages in childhood (with the vastmajority acquiring both languages by the teenage years), withhigh levels of proficiency in both languages across multiple mo-dalities, and daily use of each language, consistent with thecriteria cited by Bialystok (2009). Despite using these well-established criteria to recruit bilingual participants, we acknowl-edge that our sample was somewhat heterogeneous. Althoughheterogeneity may increase the generalizability of the results(Friesen et al., 2015), it may have contributed to the null resultsin our study and to other conflicting findings regarding the bilin-gual cognitive advantage in young adults (e.g., Bialystok, 2006;Kousaie & Phillips, 2012; Paap & Greenberg, 2013; Ratiu &Azuma, 2015). However, several visual search studies have re-ported such an advantage with college-aged participants likethose in our present samples (e.g., Friesen et al., 2015;Hernández et al., 2012).

Another possible explanation for our null results could beour relatively small sample sizes. Perhaps our data containedtrends toward a bilingual advantage, but we lacked the statis-tical power to classify such trends as reliable. The small sam-ple sizes may have contributed to larger standard deviations insome conditions making small or subtle group differencesharder to detect. To address these concerns, we includeAppendix Figs. 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 and19, which shows scatterplots of individuals’ performanceacross all conditions. These plots show that the bilingual andmonolingual groups consistently overlap, and therefore thatincreased sample sizes likely would not change these trends.Indeed, when we recruited larger samples sizes (e.g., Exp. 3),we found no reliable differences between groups. To furtherexamine these null data, we calculated scaled JZS Bayesfactor values (see Appendix Table 9). These analyses providean odds ratio in favor of the null or alternative hypothesis. Theresults show moderately strong evidence in favor of the nullhypothesis (about 3:1) in nearly all comparisons (Rouder,Speckman, Sun, Morey, & Iverson, 2009). Post-hoc poweranalyses were conducted to determine the appropriate samplesizes needed to detect differences between bilinguals andmonolinguals (see Appendixes Tables 3, 4 and 5). Over 100participants would be needed to detect an effect of speakergroup in any condition, which reflects the absence of anyrobust underlying group differences, and greatly exceeds stan-dard sample sizes in the literature.

One finding that may have implications for future studiesof bilingual cognition is that individual differences in


language experience (language balance) predicted perfor-mance across several conditions in Experiments 2 and 3.This result is consistent with previous research suggesting thatbilinguals’ language-switching experience may influence ex-ecutive function (Prior & Gollan, 2011). Bilinguals who useboth languages daily must switch between languages on amore regular basis than less-balanced bilinguals, and this ex-perience may lead to differences in how they perform nonlin-guistic tasks. However, this effect should be interpreted withcaution, given that it was not observed across all experiments.

Overall, the results of the present study did not reveal arobust bilingual advantage in visual search. If being bilingualor multilingual confers attentional, executive function, or work-ingmemory capacity advantages, a consistent difference shouldhave been observed across the present experiments. The onlyreliable group difference was observed in Experiment 3, inwhich bilinguals exhibited a disadvantage in search decision

times relative to monolinguals. We observed no apparent dif-ferences between monolinguals and bilinguals in attentionalguidance, response initiation, or overall search performance.Although bilinguals did not show a consistent visual searchadvantage relative to monolinguals, the possibility still existsthat specific aspects of the bilingual experience may be relatedto search performance (e.g., Friesen et al., 2015; Hernándezet al., 2012). Examining the contribution of bilingual experi-ence may be a challenging task, because little is known aboutwhat experiences improve executive function (e.g., Owen et al.,2010; Valian, 2015), but investigating such experiences ingreater depth may shed light on the complex relationship be-tween bilingualism and cognitive ability.

Author note The authors thank David MacKinnon for his input onpost-hoc power analyses. S.C.W. and S.D.G. were supported by NIH/NICHD Grant R01 HD075800-03 to S.D.G.

Appendix A

Table 3 Main effects and interactions for Experiment 1

F Value p Value ηp2 1 – β N Needed

Overall SearchBlackTrial Type 166.19 <.001 .856 1.000 6Search Difficulty 143.62 <.001 .837 1.000 6Speaker Group 0.26 .612 .009 .068 1,064Trial Type × Search Difficulty 15.88 <.001 .362 .947 21Trial Type × Speaker Group 0.02 .893 .001 .052 9,629Search Difficulty × Speaker Group 0.96 .388 .033 .126 286Trial Type × Search Difficulty × Speaker Group 0.31 .735 .011 .073 870

ColorTrial Type 94.93 <.001 .772 1.000 7Search Difficulty 278.40 <.001 .909 1.000 5Speaker Group 0.02 .880 .001 .052 9,629Trial Type × Search Difficulty 72.16 <.001 .720 1.000 8Trial Type × Speaker Group 0.01 .944 .000 <.050 96,341Search Difficulty × Speaker Group 0.25 .778 .009 .068 1,064Trial Type × Search Difficulty × Speaker Group 0.25 .778 .009 .068 1,064

First FixationsBlackSearch Difficulty 74.26 <.001 .726 1.000 8Speaker Group 0.02 .887 .001 .052 9,629Search Difficulty × Speaker Group 0.41 .666 .014 .080 682

ColorSearch Difficulty 199.13 <.001 .877 1.000 5Speaker Group 0.56 .459 .020 .094 476Search Difficulty × Speaker Group 1.02 .368 .035 .131 269

Decision TimesBlackSearch Difficulty 8.01 .001 .222 .697 37Speaker Group 0.27 .606 .010 .071 957Search Difficulty × Speaker Group 3.06 .055 .098 .315 92

ColorSearch Difficulty 47.18 <.001 .636 1.000 9Speaker Group 0.06 .808 .002 .054 4,811Search Difficulty × Speaker Group 1.43 .248 .050 .171 187


Appendix B

Appendix C



Overall SearchCondition 5.13 .008 .128 .378 87Search Difficulty 310.23 <.001 .899 1.000 6Speaker Group 0.03 .857 .001 .052 11,929Condition × Search Difficulty 0.49 .744 .014 .074 846Condition × Speaker Group 0.63 .537 .018 .082 656Search Difficulty × Speaker Group 0.05 .949 .001 .052 11,929Condition × Search Difficulty × Speaker Group 2.61 .038 .069 .200 166

First FixationsCondition 1.37 .261 .038 .123 307Search Difficulty 274.86 <.001 .887 1.000 6Speaker Group 0.88 .353 .025 .095 471Condition × Search Difficulty 0.48 .751 .014 .074 846Condition × Speaker Group 0.19 .828 .005 .058 2,380Search Difficulty × Speaker Group 1.11 .337 .031 .108 378Condition × Search Difficulty × Speaker Group 1.16 .333 .032 .110 366

Decision TimesCondition 16.38 <.001 .319 .894 31Search Difficulty 91.35 <.001 .723 1.000 9Speaker Group 0.10 .759 .003 .055 3,972Condition × Search Difficulty 0.84 .500 .024 .093 491Condition × Speaker Group 1.34 .267 .037 .121 316Search Difficulty × Speaker Group 0.03 .967 .001 .052 11,929Condition × Search Difficulty × Speaker Group 2.28 .064 .061 .179 189



Overall SearchUpdating Condition 21.58 <.001 .324 .968 35Search Difficulty 28.15 <.001 .385 .994 28Speaker Group 1.15 .288 .025 .105 538Condition × Search Difficulty 1.59 .149 .034 .129 394Condition × Speaker Group 2.87 .039 .060 .210 220Search Difficulty × Speaker Group 3.31 .041 .069 .241 191Condition × Search Difficulty × Speaker Group 1.70 .120 .036 .135 372

First FixationsUpdating Condition 13.80 <.001 .216 .785 56Search Difficulty 42.15 <.001 .457 .999 22Speaker Group 0.02 .900 .000 <.050 136,236Condition × Search Difficulty 1.35 .233 .026 .108 517Condition × Speaker Group 0.66 .578 .013 .077 1,041Search Difficulty × Speaker Group 2.31 .104 .044 .158 303Condition × Search Difficulty × Speaker Group 0.37 .903 .007 .064 1,939

Decision TimesUpdating Condition 35.52 <.001 .404 .997 26Search Difficulty 1.90 .155 .036 .135 372Speaker Group 6.54 .014 .114 .415 113Condition × Search Difficulty 1.36 .230 .025 .105 538Condition × Speaker Group 1.75 .158 .033 .126 406Search Difficulty × Speaker Group 1.59 .208 .030 .118 447Condition × Search Difficulty × Speaker Group 2.67 .015 .050 .177 266


Appendix D

Appendix E

Table 6 Means, standard deviations, and confidence intervals for normative measures

Raven’s Advanced Progressive Matrices Symmetry Span Task

Experiment 1

Bilingual 9.27 (2.69) [7.77, 10.77] 26.27 (8.55) [22.46, 30.08]

Monolingual 8.27 (2.99) [6.77, 9.77] 21.60 (5.54) [17.79, 25.41]

Experiment 2

Bilingual 7.83 (3.29) [6.07, 9.60] 28.00 (11.15) [22.95, 33.05]

Monolingual 9.42 (4.03) [7.70, 11.14] 29.89 (9.95) [24.98, 34.81]

Experiment 3

Bilingual 8.31 (3.57) [6.50, 10.13] 26.13 (10.12) [20.93, 31.32]

Monolingual 7.36 (3.59) [5.81, 8.91] 25.41 (10.32) [20.98, 29.84]

Standard deviations are in parentheses, 95% confidence intervals are shown in brackets.

Table 7 Means, standard deviations, and confidence intervals for Experiment 2

Visual Search Difficulty


Overall SearchColorBilingual 2,251.9 (302.5) [2,093.3, 2,410.6] 3,798.2 (726.3) [3,490.6, 4,105.8] 4,876.3 (1,104.9) [4,412.6, 5,339.9]Monolingual 2,372.6 (356.9) [2,218.1, 2,526.9] 3,926.1 (552.4) [3,626.8, 4,225.5] 4,524.7 (820.1) [4,073.4, 4,975.9]

ShapeBilingual 2,341.6 (336.5) [2,165.1, 2,518.1] 3,991.5 (916.8) [3,546.6, 4,436.3] 4,563.3 (847.0) [4,182.6, 4,944.1]Monolingual 2,347.2 (396.9) [2,175.5, 2,518.9] 3,907.9 (941.8) [3,474.9, 4,340.9] 4,640.5 (744.0) [4,269.9, 5,011.1]

SwitchBilingual 2,502.9 (381.6) [2,307.9, 2,697.8] 4,191.0 (598.6) [3,877.2, 4,504.8] 4,596.9 (845.5) [4,161.2, 5,032.6]Monolingual 2,413.9 (430.4) [2,224.2, 2,603.7] 4,160.4 (705.5) [3,855.0, 4,465.8] 5,057.5 (968.0) [4,633.4, 5,481.6]

First FixationsColorBilingual 1,541.3 (467.7) [1,353.5, 1,729.0] 2,407.5 (479.9) [2,164.9, 2,650.2] 3,121.9 (814.9) [2,797.4, 3,446.4]Monolingual 1,534.0 (304.5) [1,351.3, 1,716.8] 2,750.8 (531.6) [2,514.6, 2,986.9] 3,107.9 (516.9) [2,792.1, 3,423.8]

ShapeBilingual 1,548.4 (269.4) [1,416.4, 1,680.4] 2,711.9 (599.4) [2,412.8, 3,010.9] 3,168.7 (501.0) [2,895.1, 3,442.3]Monolingual 1,535.9 (281.8) [1,407.4, 1,664.4] 2,796.6 (648.3) [2,505.5, 3,087.7] 3,226.5 (631.2) [2,960.2, 3,492.8]

SwitchBilingual 1,564.5 (272.5) [1,439.1, 1,690.0] 2,694.5 (410.2) [2,477.0, 2,911.9] 3,026.0 (490.7) [2,744.6, 3,307.5]Monolingual 1,473.6 (252.2) [1,351.4, 1,595.7] 2,772.5 (492.5) [2,560.9, 2,984.1] 3,320.2 (667.3) [3,046.3, 3,594.2]

Decision TimesColorBilingual 850.2 (187.9) [763.3, 937.1] 1,246.5 (328.8) [1,079.9, 1,413.2] 1,669.0 (451.9) [1,439.4, 1,898.6]Monolingual 873.8 (175.4) [789.2, 958.4] 1,226.1 (365.8) [1,063.9, 1,388.3] 1,382.8 (504.8) [1,159.3, 1,606.3]

ShapeBilingual 790.4 (151.8) [700.8, 879.9] 1,117.1 (452.5) [932.6, 1,301.6] 1,255.8 (375.5) [1,038.6, 1,473.1]Monolingual 784.1 (215.2) [696.9, 871.2] 1,080.6 (309.2) [901.1, 1,260.2] 1,312.9 (321.7) [1,101.4, 1,524.4]

SwitchBilingual 993.4 (154.9) [892.3, 1094.4] 1,311.3 (252.4) [1,172.5, 1,450.1] 1,474.3 (357.2) [1,252.0, 1,696.5]Monolingual 929.8 (253.2) [831.5, 1028.2] 1,319.5 (321.7) [1,184.4, 1,454.6] 1,597.9 (546.8) [1,381.5, 1,814.2]



Appendix F

Table 8 Means, standard deviations, and confidence intervals for Experiment 3

Visual Search Difficulty


Overall Search

Control

Bilingual 2,686.6 (558.6) [2,388.5, 2,984.8] 3,495.0 (1,221.5) [3,066.3, 3,923.7] 3,644.7 (1,088.6) [3,042.0, 4,247.4]

Monolingual 3,015.6 (865.7) [2,711.1, 3,320.2] 3,089.9 (815.2) [2,651.9, 3,527.9] 4,341.3 (1,776.7) [3,725.7, 4,956.9]

Secondary Load

Bilingual 2,833.0 (816.6) [2,500.5, 3,165.5] 3,636.9 (1,422.3) [3,164.0, 4,129.8] 4,019.4 (1,017.2) [3,536.9, 4,501.9]

Monolingual 3,122.4 (800.3) [2,782.8, 3,462.1] 3,513.8 (841.0) [3,020.5, 4,007.1] 3,732.7 (1,317.4) [3,239.8, 4,225.6]

Updated Search

Bilingual 4,098.9 (1,969.6) [3,417.8, 4,780.1] 4,432.5 (1,771.3) [3,837.6, 5027.5] 4,701.1 (1,796.6) [4,081.1, 5,321.1]

Monolingual 3,426.8 (1,248.6) [2,731.0, 4,122.6] 3,585.0 (100.9) [2,977.2, 4,192.8] 4,150.1 (1,130.2) [3,516.8, 4,783.5]

Dual Task

Bilingual 4,522.8 (1,852.5) [3,893.9, 5,151.6] 5,190.4 (1,797.1) [4521.8, 5859.0] 4,694.3 (1,289.7) [4,147.4, 5,241.2]

Monolingual 3836.7 (1,094.4) [3,194.4, 4,479.1] 4,350.6 (1,425.8) [3,667.7, 5033.6] 4,827.9 (1,371.3) [4,269.3, 5,386.6]

First Fixations

Control

Bilingual 2,238.6 (474.7) [2,021.3, 2,456.0] 2,575.8 (633.1) [2,345.8, 2805.8] 2,820.4 (737.5) [2,523.9, 3,117.0]

Monolingual 2,365.0 (669.7) [2,130.2, 2,599.9] 2,609.6 (572.5) [2,361.1, 2858.0] 3,043.5 (829.9) [2,723.1, 3,363.8]

Secondary Load

Bilingual 2,221.4 (639.2) [1,976.1, 2,466.6] 2,786.0 (811.4) [2,510.3, 3,061.8] 3,031.2 (875.8) [2,699.9, 3,362.5]

Monolingual 2,416.2 (654.2) [2,151.3, 2,681.1] 2,631.4 (611.9) [2,333.6, 2929.3] 3,009.8 (869.1) [2,652.0, 3,367.6]

Updated Search

Bilingual 2,492.4 (926.5) [2,126.4, 2,858.3] 2,878.7 (835.1) [2,575.1, 3,182.2] 2,953.9 (963.9) [2,588.1, 3,319.8]

Monolingual 2,673.9 (1,006.6) [2,278.6, 3,069.2] 2,702.8 (756.3) [2,374.9, 3,030.7] 3,140.9 (963.6) [2,745.7, 3,536.0]

Dual Task

Bilingual 2,639.6 (871.1) [2,314.9, 2,964.4] 3,462.2 (1,121.4) [3,077.1, 3,847.4] 3,621.1 (957.3) [3,254.6, 3,987.7]

Monolingual 2,737.4 (836.8) [2,386.7, 3,088.2] 3,144.9 (873.1) [2,728.8, 3,560.9] 3,448.7 (975.6) [3,052.8, 3,844.7]

Decision Times

Control

Bilingual 650.9 (422.3) [513.4, 788.2] 765.3 (508.1) [619.2, 911.4] 816.6 (504.9) [647.6, 985.6]

Monolingual 611.4 (289.3) [460.5, 762.4] 562.0 (162.2) [401.4, 722.6] 681.4 (381.3) [495.6, 867.1]

Secondary Load

Bilingual 699.5 (200.6) [618.4, 780.7] 872.6 (600.8) [694.8, 1,050.5] 856.6 (482.1) [698.0, 1,015.2]

Monolingual 605.1 (237.0) [515.9, 694.3] 651.6 (255.2) [456.2, 847.1] 644.9 (343.9) [470.5, 819.2]

Updated Search

Bilingual 1,330.6 (1,090.3) [1,010.3, 1,651.0] 1,383.2 (1,124.9) [1,045.5, 1,720.9] 1,626.5 (1,009.9) [1,308.8, 1,944.1]

Monolingual 824.8 (435.7) [472.7, 1176.9] 886.7 (528.4) [515.5, 1,257.9] 1,108.5 (606.8) [759.3, 1,457.7]

Dual Task

Bilingual 1,852.4 (1,470.8) [1,430.2, 2,274.5] 1,666.0 (1,185.7) [1,278.6, 2,053.5] 1,323.9 (672.6) [1,043.8, 2,274.5]

Monolingual 1,178.2 (458.4) [714.2, 1,642.3] 1,224.1 (826.9) [798.2, 1,650.0] 1,515.0 (837.2) [1,207.1, 1,822.9]



Appendix G

Appendix H

Table 9 Scaled Jeffrey–Zellner–Siow Bayes factors for speaker group main effects across experiments

Scaled JZS Bayes Factor Odds Favor

Experiment 1BlackOverall search response times 3.41 NullFirst fixations 3.78 NullDecision times 3.41 Null

ColorOverall search response times 3.78 NullFirst fixations 3.00 NullDecision times 3.72 Null

Experiment 2Overall search response times 4.11 NullFirst fixations 2.84 NullDecision times 3.98 Null

Experiment 3Overall search response times 2.90 NullFirst fixations 4.81 NullDecision times 3.42 Alternate (M+)

The scaling factor was set to 1 as a default. M+ = Monolingual advantage.

Fig. 7 Examples of stimulus selection in the easy, medium, and difficult conditions of Experiment 1


Appendix I

A B

Fig. 8 Results from Experiment 1. Panel A shows individual search RTs in the Black Condition, panel B shows individual search RTs in the ColorCondition


A B

Fig. 9 Results from Experiment 1. Panel A shows individual first fixation times in the Black Condition, panel B shows individual first fixation times inthe Color Condition


A B

Fig. 10 Results from Experiment 1. Panel A shows individual decision times in the Black Condition, panel B shows individual decision times in theColor Condition

A B C

Fig. 11 Results from Experiment 2. Panel A shows individual search RTs in the Color Condition, panel B shows individual search RTs in the ShapeCondition, panel C shows individual search RTs in the Switch Condition


A B C

Fig. 12 Results from Experiment 2. Panel A shows individual first fixation times in the Color Condition, panel B shows individual first fixation times inthe Shape Condition, panel C shows individual first fixation times in the Switch Condition

A B C

Fig. 13 Results from Experiment 2. Results from Experiment 2. Panel A shows individual decision times in the Color Condition, panel B showsindividual first decision in the Shape Condition, panel C shows individual decision times in the Switch Condition


A B

Fig. 14 Results from Experiment 3. Results from Experiment 3. Panel A shows individual search RTs in the Control Condition, panel B showsindividual search RTs in the Secondary Load Condition

C D

Fig. 15 Results from Experiment 3. Panel C shows individual search RTs in the Updated Search Condition, panel D shows individual search RTs in theDual Task Condition


A B

Fig. 16 Results from Experiment 3. Panel A shows individual first fixation times in the Control Condition, panel B shows individual first fixation timesin the Secondary Load Condition

C D

Fig. 17 Results from Experiment 3. Panel C shows individual first fixation times in the Updated Search Condition, panel D shows individual firstfixation times in the Dual Task Condition


A B

Fig. 18 Results from Experiment 3. Panel A shows individual decision times in the Control Condition, panel B shows individual decision times in theSecondary Load Condition

C D

Fig. 19 Results from Experiment 3. Results from Experiment 3. Panel C shows individual decision times in the Updated Search Condition, panel Dshows individual decision times in the Dual Task Condition


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Comparing visual search and eye movements in bilinguals ... · Comparing visual search and eye movements in bilinguals and monolinguals Ileana Ratiu1,2 & Michael C. Hout3 & Stephen